A diabetic does not normally secrete insulin in his/her body, and thus, it is recommended that the diabetic periodically measures a blood sugar level and directly injects insulin into his/her body. As a method of directly injecting insulin into a diabetic, there are a self-injection method in which an individual voluntarily injects insulin and an automated method in which an insulin pump automatically injects insulin. For the insulin pump, a tube referred to as a needle or a cannula is injected up to a subcutaneous fat layer in order to automatically inject insulin into a body.
In this case, occlusions occur occasionally since protein or fat tissue is stuck to the end of the needle or cannula according to a defense mechanism against foreign substances coming into the body from the outside.
When a force is continuously applied by a piston, a plunger, or a pump to push drugs in an occlusion state, internal pressure of a syringe, a cartridge, and a reservoir increases, and when this phenomenon is continued, if the pressure exceeds a critical value, an occluded portion is forcibly broken, thereby injecting much insulin into the body in a short time.
In this case, due to the sudden insulin injection, a diabetic may be physically damaged, or in a severe case, the diabetic may die due to hypoglycemic shock, and thus, the necessity of quickly and accurately detecting insulin occlusion inside a fluid delivery device, such as a needle or a cannula, has increased.
When a light-emitting diode (LED) device is used in an existing apparatus for detecting fluid occlusion, there is used a method of estimating the occurrence of occlusion according to a change in the intensity of light received by a photo detector due to shape deformation of a reflective film when pressure inside a fluid reservoir device increases. However, In this case, since the LED device is used, it is difficult to continuously measure due to current consumption, and occlusion detection and a detection time varies according to a measurement period. In addition, since external light is necessarily blocked, mechanical complexity increases and many electronic parts and elements are used.
In addition, there is another existing method of detecting occlusion by disposing a conductor on a membrane expanding in response to pressure at a point through which fluid flows and allowing the conductor to function as a switch when electrified through the conductor contacting two electrodes of an upper plate due to swelling of the membrane. However, in this case, occlusion is detected when electrified, but since a pump circuit for injecting the fluid into a human body is still activated, an additional process for stopping injecting the fluid into the human body as soon as detecting occlusion is demanded.